Metal working method



United States Patent 0 METAL WORKING METHOD Robert M. Christner, BeaverFalls, Pa.

No Drawing. Application January 12, 1950, Serial No. 138,274

2 Claims. (Cl. 117-127) This invention pertains to the working of metalsand a composition of matter for use in metal-working, and relatesespecially to the working of ferrous metals. the present time theinvention has particular utility in forming operations in which themetal is worked in or over dies. It is especially useful in the colddrawing of stainless steel, and will be particularly described in thisconnection. This application constitutes a continuationin-part of myapplication Serial No. 536,847, filed May 22, 1944, and now abandoned.

In the cold drawing of ordinary low carbon steel, the steel is pickled,and upon removal from the pickling vat, is allowed to dry. The drying ofthe pickling solution on the surface of the steel leaves a light,deposit of rust which is very beneficial as a lubricant in thesubsequent drawing of the steel through a die.

In the drawing of stainless steel, however, the steel is resistant tothe action of pickling solutions, and a coating may not therefore beformed on the surface of stainless steel by pickling. When attempts aremade to draw the stainless steel, it merely sticks or galls in the die.This is especially true in the drawing of tubing over a mandrel wherethe metal is being worked on both the inner surface of the tube and theouter surface. Many attempts have been made to find a satisfactorydrawing lubricant, but materials developed for this purpose have beengenerally unsatisfactory. Consequently the present method of colddrawing stainless steel involves the coating of the steel with a film oflead. The lead coated stainless steel rod or tube is then drawn andafter completion of the drawing operation, as well as for eachintermediate annealing operation, the lead is removed by nitric acid,which acid reacts with the lead, but does not attack the stainlesssteel. This is quite an expensive operation, as well as a relativelyslow one. Moreover, it is diflicult to apply the lead to secure auniform thickness of coating, and any variation in the thickness of thelead film reflects itself in the surface of the stainless steel tube.Variations in the thickness of the lead leave waves or irregularitieswhich are sometimes referred to as lead dents which, in highly finishedstainless steel, have to be removed or rendered less conspicuous bypolishing.

Additionally, the amount of reduction in each drawing pass must besubstantially less than the reduction which can be taken in each pass inthe cold drawing of low carbon steel. Not only must the reduction beless, but the cold working using a lead film seems to rapidly producework hardening of the metal, requiring that it be annealed one or moretimes in between the initial and final drafts. It is unusual, forexample, in drawing stainless steel tubing over a mandrel to get morethan one or at most two drafts before annealing is necessary. Aspreviously stated annealing requires complete removal 2,717,221 PatentedSept. 6, 1955 2 cium oxide in water, and I also prepared separatesolutions of iron sulphate andsodium hydroxide. These solutions werethen mixed, and a reaction followedfiesultingin a solution of sodiumsulphate being formed of the lead film, as any residuum of lead willdamage the stainless steel when it is heated to annealing temperature.

According to my application hereinbefore referred to, I disclose aprocess wherein I prepared a mixture of calalong with a precipitatewhich was ferrous oxide. The precipitate so formed was mixed with thecalcium hydroxide mixture first prepared, and this was applied to thesurface of the metal to be drawn. I have since discovered in workingwith my invention as there disclosed, that I had not completely removedthe sodium sulphate from the ferrous hydroxide, and when the ferrousoxide so contaminated with sodium sulphate was mixed with the calciumhydroxide or lime water preparation, calcium sulphate was formed in alimited amount, and the calcium sulphate was the important factor withthe iron compound that resulted in the exceptional lubricatingproperties of the material which I used. This developed from experimentswherein I tried to remove completely, by thorough washing, all sodiumsulphate from the iron hydroxide. I then discovered that the compoundwas less effective than where the precipitate was not free of the sodiumsulphate. Thus, while my original practice of having a mixture comprisedpredominately of iron hydroxide and lime gave a successful drawingoperation, I have found that substantially better results are obtainedwhere the iron hydroxide is associated principally with calciumsulphate. Of special importance therefor is the ferrous hydroxide whichis converted upon application to the surface of the iron which upondrying in the air changes from the ferrous to ferric compound, while thecalcium sulphate or the lime have a complementary action, the sulphate,.for reasons unknown to me, give a much better body and adhesion thanthe lime, making a greater number of draws possible with one coating.

According to the preferred practice of the present invention, Ipreparelime water by introducing lime into water. I separately dissolveiron sulphate in water. I then bring the two mixtures together andagitate them. This results in the precipitation of hydroxide of iron andcalcium sulphate as a single compound, or with the calcium sulphate andiron hydroxide in intimate physical association. 1

Enough lime is used in the water so as to form a rather heavysuspension. The solution of iron sulphate is a highly concentratedsolution, it being desirable that the calcium sulphate and ironhydroxide be in a rather creamlike slurry. Enough lime is used tocompletely convert all of the iron sulphate, but the proportions are notcritical, and there may be in the finished product unreacted lime.

After the reaction resulting from the mixture of the lime water and thesolution of iron sulphate, the material is then ready to-use. Thecalcium sulphate and iron hydroxide which tend to precipitate canbe keptin suspensionby agitation of the mixture, and the articles to be drawncan be dipped into this liquid slurry.

As an alternative, after the reaction has been effected, excess watermay be removed by evaporation, reducing the mass to a thick, paste-likecondition, which can be put into drums and shipped and sold as acommercialmaterial soap, soap powder or other lubricant being mixed withthe reaction product. Roughly about 50% of the mix is soap, but theseproportions are not critical, .but without soap the product will notcold work satisfactorily or'remain on the surface of the metal. Soap ofa type commonly used in the art has a base consisting of the sodium saltor oleic, stearic or palmitic acid or mixtures thereof, and such soapmay or may not be mixed with sodium or potassium carbonate. Thepurchaser remixes the paste with two or three parts of water to convertit back into a slurry. This is the preferred way of distributing theproduct commercially.

I may state that the paste which is so formed has a green color, but ifit is allowed to dry in contact with the air, it turns brown. Likewise,when tubes or other products to be drawn are dipped into the slurry andthen dried in the open air, the deposit on the surface of the tubes willlikewise turn brown.

Instead of partially evaporating the water, the precipitate may beseparated entirely from the water and dried. It can be dried to a brownpowder. This powder will have no quality of adhering to the surface ofstainless steel, but the powder can be advantageously mixed with drysoap powder lubricant of the type used in drawing stainless steel wire,and the lubricant, when so mixed with the dried compound above referredto, will perform much more satisfactorily, especially in the drawing ofstainless steel wire which has previously also been coated with theslurry and then dried in the air.

Acccording to my invention, therefore, the reaction product obtained bythe mixing of calcium hydroxide and iron sulphate, and preferablycarrying some free lime, is used as a lubricant either by being firstdried and then put into the lubricant box of a drawing bench, or bybeing applied to the surface of the stainless steel as a slurry which isthen air dried, Being applied in this fashion, it intimately clings tothe surface of the stainless steel and provides a drawing or lubricatingcompound which is highly efiective, and which enables stainless steel tobe drawn with drastic reductions, without lead coating the stainlesssteel, and with less intermediate annealing than is presently required.

I prefer to use iron sulphate and lime for the preparation of thedrawing compound, because these are readily available, cheap, and highlysatisfactory. However, I

have reason to believe that the hydroxides or other alkaline earthmetals such as magnesium, barium and strontium could be used in place ofcalcium oxide or hydroxide, and that the sulphate of other neutral orsubstantially neutral or non-basic metal could be used in place of ironsulphate, as for example cadmium sulphate, nickel sulphate, or cobaltsulphate.

Also, the process disclosed in my original patent application may beused wherein iron sulfate is reacted with sodium hydroxide toprecipitate ferrous hydroxide, or other base such as ammonium orpotassium hydroxide. The ferrous hydroxide so produced may then be mixedin waterwith lime to form a slurry, or the ferrous hydroxide may bemixed with a generally but not necessarily equal part of soap. The ironhydroxide and soap can be used as such, but as stated above, it is lesssatisfactory than when lime is also added, and particularly lesssatisfactory than where calcium sulphate is also present.

In the foregoing description I have referred especially to the drawingof stainless steels, and for this purpose I know of no comparable methodor material. My invention, however, is not limited to true stainlesssteels, but is applicable also to the drawing of other steels, includinglow carbon steel and steels having a high-content of nickel and chromiumor other alloy ingredients, so long as the steels are of the type whichmay be drawn.

As hereinbefore indicated, the use of a drawing composition as hereindescribed enables stainless steel to be drawn with about the samefacility as ordinary steels are now drawn; the reduction in each draftmay be substantially heavier than where a film of lead is used, andcomplete reduction may frequently be made without intervening annealingor normalizing and where annealing is necessary the coacting substanceneed not be removed. Why the material retards the Work hardeningproperties of the stainless steel when being drawn is not known to me,but is an observed fact. As many as six drawing passes in the formationof stainless steel tubes, and with substantial reductions in several ofthe passes, have been effected without intervening heat treatment. Ihave referred especially to the drawing of tubes, because this is themost diflicult, but the invention applies likewise to drawing stainlesssteel rods and wire.

While the composition has application primarily to the drawing of steelsand particularly stainless steels, I believe that the composition mayalso have utility in the piercing of stainless steel billets, thelubrication of dies in which metals are shaped, and may be usefullyemployed in the coating of molds in which metals are cast, and believethat the composition may be advantageously used with non-ferrous metals.

While 5 have illustrated and described certain embodiments of myinvention and have specifically mentioned certain materials it will beunderstood that this is not by way of limitation, but by way ofillustration, and that various substitutions and modifications may bemade within the contemplation of my invention. Once the surfacecondition which is created by the use of my invention has been observed,one skilled in the art may readily select equivalent materials andproperties to give like satisfactory results.

it should be noted that by forming the calcium sul phate and the ferroushydroxide together in one reaction, the precipitate has a high bulkfactor; higher than would be obtained by merely mixing togetherseparately formed calcium sulphate and ferrous hydroxide, and that thereis a more intimate physical association and union of these componentswhere this reaction is used to ob.-

tain the compound. The reaction is indicated .as follows:

CalUH)sFeSOs=CaSO4+Fe(OH)z Both the calcium sulphate and the ferroushydroxide are relatively insoluble in the aqueous environment, andprecipitate as a single mass. As above indicated, suflicient lime isused so that there may .be some calcium oxide in the resulting mix, butthis would be only a small and unimportant percentage. Also it may bepointed out that the compound may be mixed with soap or other lubricanteither in the dry form above described, or as a paste.

I claim:

in the process of drawing stainless steel the steps which comprisecoating the steel with a slurry formed of water and the reaction productof ferrous sulphate and lime in water in substantially stoichiometricamounts, drying the slurry on the stainless steel to form a coatingthereover and during which drying the iron compound present is oxidizedby contact with air.

2. In the process of drawing stainless steel, the steps which comprisemixing a solution of ferrous sulphate and sufficient lime to completelyreact the ferrous sulphate and produce a slurry which is predominantlythe reaction products of the ferrous sulphate and lime, but in whichthere may be an unimportant amount of unreacted lime, applying theslurry so formed to the surface of the stainless steel and drying thesame in air before drawing the steel and thereby effecting the oxidationin situ of the ferrous compound in the coating so formed to the ferriccompound.

References Cited in the file of this patent UNITED STATES PATENTS1,801,542 Harth Oct. 11, 1932 1,902,493 Dantsizen Mar. 21, 19331,916,677 Lloyd July 4, 1933 2,238,738 Hurd Apr. 15, 1941 2,394,620Leonard Feb. 12, 1946 FOREIGN PATENTS 42,944 France Oct. 16, 1933

1. IN THE PROCESS OF DRAWING STAINLESS STEEL THE STEPS WHICH COMPRISECOATING THE STEEL WITH A SLURRY FORMED OF WATER AND THE REACTION PRODUCTOF FERROUS SULPHATE AND LIME IN WATER IN SUBSTANTIALLY STOICHIOMETRICAMOUNTS, DRYING THE SLURRY ON THE STAINLESS STEEL TO FORM A COATINGTHEREOVER AND DURING WHICH DRYING THE IRON COMPOUND PRESENT IS OXIDIZEDBY CONTACT WITH AIR.